This invention relates to a modular connector system and in particular to a system wherein connector modules with high contact density are surface mounted to printed circuit boards.
A connector module generally comprises a housing of electrically insulative material which accommodates a plurality of contact elements or terminals arranged in rows and columns. The contact elements have a base section and a contact end and connecting end extending from opposite ends of the base section. The connecting ends project outside one side of the housing and are connected to a printed circuit board.
There have long been attempts to accommodate electronic circuits in as modular a design as possible on printed circuit boards of standard dimensions. The interconnections between the individual modules and components, such as recorders, playback devices, etc., are preferably made via electronic connectors. As a consequence of miniaturization and due to the high density of present day integrated circuits, a large number of electronic components can be mounted on a printed circuit board so that a large number of functions can be carried out by a module of this type. The number of terminals needed for connection to other modules has, likewise, increased.
As a result, there is a great need for connectors with a high contact element density, i.e., with a large number of electrical contacts or terminals per unit of volume. The need for connectors with high contact element density has become even greater as a result of the advent of surface mounting technology whereby electronic components are surface mounted to the printed circuit board. Surface mounted devices (SMD) are not mounted on a printed circuit board via the usual pinhole connection but are connected directly to the surface of the printed circuit itself. By surface mounting techniques, it is possible to mount electronic components readily on either surface of a board without interfering with connecting pins which project through the board. This results in a component density which is even higher than that achieved with conventional pinhole connections and a further increase in the number of terminals.
In many cases the contact element density of a connector cannot be increased simply placing the contact elements closer together or by forming several rows of contact elements located above one one another. Generally, this results in an undesirable mutual electrical interference between the contact elements, essentially as a consequence of capacitive couplings between them. Furthermore, it is not possible in a connector to use an unlimited number of rows located above each other because contact elements with very long connecting ends to the printed circuit board will increase problems due to the occurrence of undesired inductive couplings and the circuit becomes more sensitive to electromagnetic noise signals.
It is futhermore necessary to maintain a defined minimum distance between the individual contact elements because the wall thickness of the housing in which the contact elements are accommodated must not become too thin in order to meet specified strength requirements. Moreover, from the viewpoint of mechanical strength of the printed circuit board, it is not desirable to connect several rows of contact elements to only one of its sides because with such an asymmetric arrangement, the board will tend to bulge in the center of the connector. This will result in an undesired force being applied to the board which may cause breaks in the thin printed circuit strips on the board.
One attempt to solve some of these problems is disclosed in U.S. Pat. No. 4,607,907 granted Aug. 26, 1986 to Robert Bogursky. FIG. 1 of this patent shows a contact element in which a tongue-shaped solder end extends from a U-shaped base section and projects, after mounting of the contact element, outside the connector for connection to a printed circuit board. In the case of a connector with several rows of contact elements arranged above each other, such as shown in FIG. 8 of this patent, the connecting ends of contact elements located in a column above each other are connected, by soldering, one behind the other to the printed circuit board in the direction facing away from the housing. As a result, the uppermost connecting end, as viewed from the printed circuit board, is relatively long and has therefore a large leakage inductance. To have sufficient room for the circuit tracks available on the printed circuit board for soldering of these connecting ends which are located one behind the other an increase in the number of contact elements in a row the mutual distance between these will have to be larger because from a design viewpoint and in order to obtain reliable connections, the width of the circuit tracks to these connecting ends must not be too small.